Momentum - November 2017 - 19

TODAY'S

ENGINEERING

CADILLAC PLUGS IN CT6 FOR
HIGH-VALUE EFFICIENCY
The badge on the decklid reads '2.0E',
with no giveaway that the 2018 Cadillac
CT6 we're driving is a plug-in hybrid.
Perhaps a more appropriate nameplate
should be CT6 NEV, because this
impressively engaging and efficient
luxury sedan is mostly aimed at China's
burgeoning New Energy Vehicle market.
In fact, the plug-in version is assembled
only in Shanghai and exported to the U.S.
Initial stateside volumes will be only 1000
units/year. It would not be surprising to
find more American customers who see
the CT6 plug-in's almost ideal balance
of EV range (31 mi in optimal thermal
conditions), EV top speed (78 mph);
acceleration (0 to 60 mph in 5.2 s); EPA
rated efficiency (62 mpg-e); total range
(442 mi), top speed (150 mph) and
retail price ($75,095) as adding up to a
compelling value proposition.
"We weren't trying to make this a
super-long-range electric vehicle,"
noted Mike Kutcher, the lead vehicle
development engineer. "Combining the
335-hp 2.0-L turbo with the plug-in
hybrid propulsion system gives V6 twinturbo performance with pure-electric
range that's equal to about 75% of a
typical commute."
Kutcher, a veteran of GM's pioneering
hybrid and EV development group, added
that the 31-mile capability is also China's
threshold for NEV purchase incentives.
Kicking off the PHEV development
four years ago, the team was fortunate
to build upon the most mass-efficient
vehicle in its class (thanks to an
aluminum-intensive, mixed-materials
structure). About 600 lb was added,
mainly in the liquid-cooled, 18.4-kW·h
lithium battery pack located behind
the rear seat bulkhead, plus power
electronics, wiring and attendant
hardware. The production car's 4530-lb
curb weight is handily lighter than the
Cadillac's BMW, Mercedes and Porsche
PHEV competitors.
Typically, the German plug-ins differ
from the CT6 in using stepped-gear

MOMENTUM

Hybrid system layout in the
Cadillac CT6 PHEV. The 400-lb
lithium battery pack features 192
liquid-cooled cells. GM claims
4.5-h charging time on 220-V
Level 2.
(Image credit: GM)

transmissions with an electric motor
located in the P2 (between flywheel
and trans) configuration. "This results in
the electric motor amplifying the gear
changes, up and down through as many
as eight ratios multiple times per driving
event," Kutcher observed.
By comparison, the CT6 arrangement
that uses GM's electrically variable
transmission (with two 90-kW/100-hp
motors) felt seamless and refined during
Automotive Engineering's 70-mi (112-km)
test route on public roads in rural Michigan.
The GRE (Global Rear-drive Electric)
unit is unique, noted Jason Mullins, the
hybrid propulsion calibration manager
that joined Kutcher and me on our test
drive. "Having the two motors, three
planetary gearsets and five clutches gives
lots of mechanical advantage," he said.
"We call our approach 'blended PHEV'
with the automated controls executing
all commands in real time. When full,

the battery provides primary power and
blends in the ICE for supplemental power
based on pedal input."
At 45-50% pedal travel, the system's
electric-only capability ends and the
ICE engages smoothly for supplemental
torque. When the battery is depleted (at
a bit over 31 miles during our summer test
drive), the car operates like a conventional
HEV. Among the three drive modes, Tour
provides the most EV capability; Sport has
a more aggressive pedal map and sportier
steering, and the Hold mode will save the
battery-only operation for when you want
it later, such as entering a city after a long
interstate trip.
"We were watching the trend for
'low emission zones' in urban areas,"
Kutcher explained. "The feature may offer
opportunity for compliance."

By Lindsay Brooke, Automotive Engineering

November 2017 19
Momentum - November 2017

Table of Contents for the Digital Edition of Momentum - November 2017
